As known in the art, communication systems have been developed based on voice service and are now advancing to providing data service and various multimedia services as well as voice service. However, conventional communication systems have not satisfied users' service demands because of their relatively narrow bandwidths and expensive fees. Additionally, advances in the communication industry and users' increasing demand for Internet service raise the necessity for communication systems that efficiently provide Internet service. As a result of these trends, broadband wireless communication systems are used to efficiently provide Internet service.
Using orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme, the broadband wireless communication system can realize a high-speed data transmission by sending a physical channel signal using subcarriers. The wireless access scheme of the broadband wireless communication system is standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standardization group, which is an international standardization organization.
Typically, wireless data communications are subject to data error according to conditions of a radio channel. Error control and recovery methods include an Automatic Repeat reQuest (ARQ) scheme and a Forward Error Correction (FEC) scheme.
A HybridARQ (HARQ) scheme combines the ARQ and FEC schemes. According to the ARQ scheme, a receiver checks for error in the received packet through a Cyclic Redundancy Check (CRC) and feeds a retransmission request to a transmitter upon detecting the error, and the transmitter retransmits the corresponding packets. According to the FEC scheme, the transmitter transmits packet by adding redundancy information to the data through coding, and the receiver corrects for error in the received packet using the redundancy information.
By taking advantage of the above schemes, the HARQ scheme can correct error below a certain degree using the FEC scheme and correct error above the certain degree using the ARQ scheme. The HARQ scheme includes a Chase Combining (CC) scheme and an Incremental Redundancy (IR) scheme. According to the CC scheme, the transmitter retransmits initial transmit packets in the event of a failure of the initial transmission, and the receiver combines (or soft-combines) and decodes symbols from the initial transmit packets and the retransmit packets to obtain the gain due to the increase of the Signal to Noise Ratio (SNR). The IR scheme initially transmits some redundancy data of the encoded data and information data and additionally retransmits redundancy data not transmitted in the initial transmission. That is, the IR scheme transmits data at a low code rate in the initial transmission and increases the code rate in every retransmission to obtain an additional coding gain.
In broadband wireless communication systems, when the received HARQ burst is corrupted, the receiver feeds a retransmission request (NACK) feedback to the transmitter, and the transmitter retransmits the corresponding HARQ burst. The HARQ burst includes a plurality of Media Access Control (MAC) Packet Data Units (PDUs) of the same Modulation and Coding Scheme (MCS) level. One HARQ burst is encoded by dividing the HARQ burst into at least one FEC block. Each MAC PDU can include a code for error checking (e.g., CRC code) the ARQ of the MAC layer. Accordingly, the MAC layer can detect an erroneous MAC PDU through the error checking on each MAC PDU. However, since the physical (PHY) layer checks for error in the entire HARQ burst, it cannot acquire the location and the number of the erroneous MAC PDUs. Thus, the PHY layer performs the HARQ combination for the retransmitted HARQ bursts, divides the combined data into FEC blocks, and then decodes the data.
As discussed above, the PHY layer HARQ-processes the entire HARQ burst because the PHY layer cannot know the erroneous part (i.e., the location and the number of the MAC PDUs) of the HARQ burst. In this situation, an FEC decoder (or channel decoder) is subject to the bottleneck. As the system employs a plurality of FEC decoders to achieve a given data rate, a size increase or performance degradation of the receiver may result.